The present disclosure relates to an image reading device and an image forming apparatus.
Image forming apparatuses such as copiers and multifunctional peripherals (hereafter referred to as MFPs) are equipped with an image reading device which reads a document and generates image data. The image reading device is provided with a light source, an image sensor, an amplifier, an A/D converter, etc., for example.
The light source generates light with which a target document is to be irradiated. The image sensor receives document-reflected light, which has been reflected from the document, and outputs analog signals according to the amount of the document-reflected light received. The amplifier performs amplification processing on the analog signals received from the image sensor. The A/D converter performs A/D conversion processing on the analog signals amplified by the amplifier.
In such an image reading device, a gain set value of the amplifier is obtained (hereafter referred to as “gain setting processing”) at a time of turning on a main power supply or when returning from a sleep mode. In the gain setting processing, the amplification processing and the A/D conversion processing are performed on analog signals generated by the image sensor in reading a white reference board that is used for shading correction. Then, based on the image data (after the A/D conversion) obtained through reading the white reference board, the gain set value of the amplifier is obtained. Then, in a reading job, the gain of the amplifier is adjusted to the value obtained through the gain setting processing.
Here, conventionally, there have been known image reading devices equipped with two reading mode, that is, a color mode in which color image data is generated and a monochrome mode in which monochrome image data is generated. In such image reading devices, used as the image sensor is a four-line image sensor which includes three line sensors for the color mode (hereafter referred to as “color sensors”) respectively corresponding to R, G, and B, and a line sensor for the monochrome mode (hereafter referred to as “monochrome sensor”).
Also, there are some cases where a common image data path is used in both the color mode and the monochrome mode. In such a case, the three color sensors each have an amplifier and an A/D converter connected thereto. That is, the analog signals from the three color sensors are outputted to different image data paths to undergo the amplification processing and the A/D conversion processing. Analog signals from the monochrome sensor are outputted to one of or a plurality of image data paths for the color mode. Thus, one or a plurality of the amplifiers (the A/D converters) used for the color mode are used in the monochrome mode as well.